1. Field of the Invention
This invention generally relates to beam deflection circuits for cathode ray tubes, and more particularly is directed to an improvement in centering circuits employed for the beam deflection circuit.
2. Description of the Prior Art
In display devices utilizing a cathode ray tube, such as television receivers, in which a beam deflection circuit is provided for deflecting an electron beam in the cathode ray tube to produce a raster on a screen of the tube, it is required to move or shift the position of the raster on the screen in order to center a picture on the screen. To meet this requirement, a centering circuit which usually works in cooperation with the beam deflection circuit is provided in the display device.
There have been proposed several centering circuits employed for, for example, a horizontal deflection circuit of the television receiver. The prior art centering circuit previously proposed is composed of a variable resistor acting to control a centering current flowing through a horizontal deflection coil for centering the picture on the screen and a switch device connected to switch the direction of the centering current, and supplies to the horizontal deflection coil with the centering current having a direction selected by the switch device in response to the direction of shift of the raster and a value controlled by the variable resistor in response to the amount of shift of the raster in the horizontal direction. Such a centering circuit as mentioned above, however, has a disadvantage that it is relatively troublesome to set the raster at an appropriate position because of selecting the direction and controlling the value of the centering current. Further, in this case, the value of the centering current is controlled by the variable resistor, so that the power dissipated in the variable resistor is relatively much.